Right, this is missing in the docs.
When the button is pressed for a small interval, the currently running program is stopped. This can be disabled by enabling the command line argument
--disable-cape-button-monitoring. You will have to go to your project settings in the IDE, and add
--disable-cape-button-monitoring to the field "User command line arguments".
When the button is pressed for more than 2 seconds, a graceful shutdown is triggered. This can be disabled by removing / renaming / emptying/ commenting out the content of the file
/root/Bela_capeButtonHold.sh. So the quick way is
$ rm /root/Bela_capeButtonHold.sh
But if you plan to do restore the functionality later, you may prefer to comment out with a
# the two lines in the file, instead.
These should do it for now, I will look into putting this into the docs properly.